Method of manufacturing sponge rubber



a the mixing in the mill is practically comtime during the mixing operation, but as ated as heat is again generated between the sured. After the mixing is completed the 90 Patented Sept; 15, 1931 a v 1,823,335

* UNITED, STATES PATENT OFFICE PAUL H. BIOHERT, or BERKELEY, CALIFORNIA METHOD or MANUFACTURING SPONGE RUBBER I No Drawing. Application filed April 29, 1929. Serial No. 359,176.

This invention relates to a method of gassing agent is employed which decomcompounding or preparing rubber preparaposes at comparatively low temperatures, tory to vulcanizing the same, and especially for instance, a temperature of 160 to 180 to a method of compounding or preparing Fahrenheit is often reached in the mixing 6 rubber intended for the manufacture of mill, and if a gassing agent of this charsponge rubber articles and the like. acter is employed it starts to decompose or In the manufacture of sponge rubber a evolve gas at or near such temperatures. gassing agent or compound capable of lib- Gas losses anda variable product are thereerating gases at the temperature of vulcanfore only to be expected.

10 ization is required, as it is the gas liberated I have also discovered a gassing agent that produces the cellular structure characwhich will not decompose below 200 Fahteristic of sponge rubber. renhelt, and when an agent of this charac- A number of gassing agents have been ter is used it is possible to obtain a finished employed, such as ammonium carbonate, sponge rubber of uniform cellular struc- 15 etcetera, but they are not altogether satisture, and possessing cells closely approachfactory as decomposition and liberation of ing a predetermined number and size per gas takes place to a large extent prior to unit of volume; vulcanization. That is, considerable heat is The gassing agents or compound emevolved, while the rubber is being plastiployed are sulfites of ammonia, such as: y 20 (hi beglveen the m xipg rolls ofda mtill, anld I Ammonium sulfite (NH4)2SO3 H2O w 1 e 0 er compounc mg ingre 1en s suci Ammonium bi sulfite NHLLHSOS as fillers etc. are bein added.

In order to insure the retension of at least Ammonmm meta bbsulfite (NHOZSZOJ a minimum amount of gas liberating conor any compound of this character which 25 stituents during the mixing operation, it has will decompose under a vulcanizing temperbeen customary to use a largeexcess of the ature, but remain stable below or near 200 material. This not only causes a waste of Fahrenheit; material, that is the gassing agent, but a 'In the preparation of rubber for the manufar more serious result is variation in refacture of sponge rubber articles I add ap- 30 suits, as successive batches due to more or proximately two pounds of ammonium sul- 3 less liberation of gas prior to'vulcanization fite to sixty pounds of the rubber compound differ in quality and texture. In other into be employed. The ammonium sulfite is stances the gassing agent is not added until preferably ground, and may be added at any i 35 pleted. Even then it is necessary to rerun there is no danger of decomposition taking 35 the entire batch to insure thorough distribuplace, it is preferable to add it before the tion of'the gassing agent throughout the addition of other compounding ingredients "entire mass. Time is lost by this method if they are employed, as thorough distribu+ of mixing, a certain amount of gas is libertion and ,a uniform product is thereby in-' mixing rolls, and the final result is again compounded material is ready for vulcanvariable. I ization in the usual manner.

Due to the fact that gas is liberated in The proportions of gassing agent to rubvarying quantities regardless of the mixher, as above stated, may be varied over a ingmethod employed, it is practically imwide range, depending upon the number of possible to obtain a finished sponge rubber cells desired per unit volume and the size of product having a predetermined cellular the cells may be varied by grinding the structure or texture. I gassing compound coarser or finer, the {I have discovered that the gas losses encoarser ground material producing larger countered are entirely due to the fact that a cells.

2;; i i r 1,823,335

In actual practice I have found that the gassing agent employed is suitable for a great variety of sponge rubber articles, such as semi-hard sponge rubber, soft sponge rubber etc.

It is accordingly understood that I do not limit myself solely to one variety or another,

. nor to sponge rubber alone, as the gassing agent may be employed whenever it is desired to incorporate a material whose decomposition below the vulcanizing temperature isto be avoided.

Having thus described my invention, what claim and desire to secure by Letters Patent 1. The; herein described method of forming cells in rubber during vulcanization thereof which consists in introducing into the rubber during plasticization thereof a sulfite of ammonia, and then subjecting the rubber to suflicient temperature to decompose the sulphite: of ammonia and to' vulcanize the rubber.

2. The herein described method of forming cells in rubber during vulcanization thereof which consists in introducing into the: rubber during plasticization thereof a ground. sulfite of ammonia, and then subj ecting the rubber to sufficient temperature to decompose the sulphite of ammonia and to vulcanize the rubber; V

3. The herein described method. of forming cells in rubber during vulcanization thereof which consists in introducing into. the rubberduring plastici-zation thereof a ground ammonium bi-sulphite, and then subjecting therubber tosuflicient temperature to decompose the bi-sulphite and to vulcanize the rubber.

14.. In the. manufacture of sponge rubber, the methodof forming cells in the rubber which comprises adding to the rubber a sulphite of ammonia during theplasticizati'on thereof, and subsequently exposing" the combination of said rubber and said suphite of ammonia to: a volatilizing temperature.

PAUL H. RICH'ERT. 

